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    <title>卫星成像过程 | Mars3D | 三维地图 | 火星科技 | 合肥火星科技有限公司</title>

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    <script
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      include="jquery,font-awesome,bootstrap,layer,haoutil,turf,mars3d"
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  <body class="dark">
    <!--加载前进行操作提示，优化用户体验-->
    <div id="mask" class="signmask" onclick="removeMask()"></div>

    <div id="mars3dContainer" class="mars3d-container"></div>

    <script src="./js/common.js"></script>
    <script type="text/javascript">
      "use script"; //开发环境建议开启严格模式

      var map;
      var graphicLayer;

      function initMap(options) {
        //合并属性参数，可覆盖config.json中的对应配置
        var mapOptions = mars3d.Util.merge(options, {
          scene: {
            //此处参数会覆盖config.json中的对应配置
            center: { lat: 40, lng: 111.833884, alt: 20000000, heading: 0, pitch: -90 },
            cameraController: {
              zoomFactor: 3.0,
              minimumZoomDistance: 1,
              maximumZoomDistance: 300000000,
              constrainedAxis: false, //解除在南北极区域鼠标操作限制
            },
          },
        });

        //创建三维地球场景
        map = new mars3d.Map("mars3dContainer", mapOptions);

        //创建矢量数据图层
        graphicLayer = new mars3d.layer.GraphicLayer();
        map.addLayer(graphicLayer);

        haoutil.loading.show();

        var czml = Cesium.CzmlDataSource.load("//data.mars3d.cn/file/czml/satellite-one.czml");
        czml
          .then(function (dataSource) {
            haoutil.loading.close();

            map.dataSources.add(dataSource);

            let satelliteEntity = dataSource.entities.values[0];

            var swathWidth = swathWidthDict[satelliteEntity.id];
            satelliteFoot.start(satelliteEntity, swathWidth);
          })
          .otherwise(function (error) {
            haoutil.alert(error, "加载数据出错");
          });
      }

      //多个卫星时可以可配置【卫星地面投射圆半径，足迹宽度】
      var swathWidthDict = {
        "Satellite/CBERS 4": 650000.0,
      };

      // 地球观测的轨道预测,包含绘制卫星到地球的足迹功能。
      var satelliteFoot = {
        start: function (entity, instrumentFOV) {
          if (!instrumentFOV) {
            //默认值；
            instrumentFOV = 2000 * 1000;
          }

          var secondMultiplier = instrumentFOV / 250000.0; // 每间隔多少公里进行显示一次足迹。
          var intervalBetweenFootPrints = 40 * secondMultiplier; //setInterval间隔脚印的时长
          var numberOfFootPrintsAtAtime = parseInt(90 / Math.ceil(secondMultiplier)) * 5; //保持足迹的数量个数

          var point = mars3d.LatLngPoint.fromCartesian(entity.position, map.clock.currentTime);
          this.drawOneFoot(point, instrumentFOV);

          var timeLast = map.clock.currentTime.secondsOfDay + intervalBetweenFootPrints;

          map.on(mars3d.EventType.clockTick, (event) => {
            var sxTimes = Math.abs(map.clock.currentTime.secondsOfDay - timeLast); //剩下时长

            if (sxTimes < 1 || sxTimes > intervalBetweenFootPrints) {
              console.log(sxTimes);

              timeLast = map.clock.currentTime.secondsOfDay + intervalBetweenFootPrints;

              if (graphicLayer.length >= numberOfFootPrintsAtAtime) {
                graphicLayer.clear();
              }

              var point = mars3d.LatLngPoint.fromCartesian(entity.position, map.clock.currentTime);
              this.drawOneFoot(point, instrumentFOV);
            }
          });
        },

        //绘制一个足迹
        drawOneFoot: function (point, instrumentFOV) {
          //卫星到地面的垂直线
          this._drawLineGroundToSatellite(point);

          //投射圆锥体
          this._drawInstrumentFootPrintSwathWidth(instrumentFOV, point);

          // 在地球表面上绘制可见足迹椭圆
          this._drawVisibleFootPrint(point);
        },

        //卫星到地面的垂直线,point: 卫星在天空中的位置
        _drawLineGroundToSatellite: function (point) {
          var groundPoint = Cesium.Cartesian3.fromDegrees(point.lng, point.lat, 0.0);

          var point1 = new mars3d.graphic.PointPrimitive({
            position: point,
            style: {
              pixelSize: 2,
              color: Cesium.Color.RED,
            },
          });
          graphicLayer.addGraphic(point1);

          var point2 = new mars3d.graphic.PointPrimitive({
            position: groundPoint,
            style: {
              pixelSize: 2,
              color: Cesium.Color.RED,
            },
          });
          graphicLayer.addGraphic(point2);

          var primitiveLine = new mars3d.graphic.PolylinePrimitive({
            positions: [point, groundPoint],
            style: {
              width: 1,
              color: Cesium.Color.YELLOW,
            },
          });
          graphicLayer.addGraphic(primitiveLine);
        },
        //投射圆锥体
        _drawInstrumentFootPrintSwathWidth: function (instrumentFOV, point) {
          var primitive = new mars3d.graphic.CylinderPrimitive({
            name: "视锥体",
            position: Cesium.Cartesian3.fromDegrees(point.lng, point.lat, point.alt / 2),
            style: {
              length: point.alt,
              topRadius: 0.0,
              bottomRadius: instrumentFOV,
              color: Cesium.Color.GREEN.withAlpha(0.3),
              outline: true,
              outlineColor: Cesium.Color.RED.withAlpha(0.5),
            },
          });
          graphicLayer.addGraphic(primitive);
        },
        // 在地球表面上绘制可见足迹椭圆（红色外圈线）
        _drawVisibleFootPrint: function (point) {
          var groundPoint = Cesium.Cartesian3.fromDegrees(point.lng, point.lat, 0.0);

          var radiusOfEarth = Cesium.Cartesian3.distance(new Cesium.Cartesian3(0, 0, 0), groundPoint);
          var satToOrignEarth = radiusOfEarth + point.alt; // point to origin of earth
          var groundPointToSatPointToTangentAngle = Cesium.Math.toDegrees(Math.asin(radiusOfEarth / satToOrignEarth));
          var groundPointToOriginToTangentAngle = 90.0 - groundPointToSatPointToTangentAngle;
          var distanceAlongGround = Cesium.Math.TWO_PI * radiusOfEarth * (groundPointToOriginToTangentAngle / 360.0);

          var primitive = new mars3d.graphic.CirclePrimitive({
            name: "可视卫星范围（45度）",
            position: groundPoint,
            style: {
              radius: distanceAlongGround,
              color: "#ff0000",
              opacity: 0.1,
              outline: true,
              outlineColor: "#ff0000",
            },
          });
          graphicLayer.addGraphic(primitive);
        },
      };
    </script>
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